Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $173.85   12.220%   $195.0945   $195.09   $195.10   $195.10  
  Purchase #2 $235.42   13.276%   $266.6744   $266.67   $266.65   $266.70  
  Purchase #3 $51.86   6.209%   $55.08   $55.08   $55.10   $55.10  
  Purchase #4 $114.34   8.486%   $124.0429   $124.04   $124.05   $124.00  
  Purchase #5 $138.41   8.874%   $150.6925   $150.69   $150.70   $150.70  
  Purchase #6 $221.58   8.218%   $239.7894   $239.79   $239.80   $239.80  
  Purchase #7 $50.28   4.858%   $52.7226   $52.72   $52.70   $52.70  
  7 purchase totals = $985.74       $1,084.0963   $1,084.08   $1,084.10   $1,084.10